Free piston type accumulators are not in and of themselves new, and the utilization of such accumulators in hydraulic systems is well known. Nevertheless, the present invention provides a new accumulator design especially designed for a new use within the context of a generator seal oil system.
Demanding requirements for safety, reliability and maintainability in power stations with relatively low differential pressure generator seal oil systems mandate protection schemes designed to maintain the integrity of single radial oil film gas seals applied to large steam turbine generators or gas turbine generators which are hydrogen cooled. The need for additional protection against transient disruptions of oil pressure to the air/hydrogen seal rings is occasionally driven by customer requirements and customer failure criteria that are more demanding than has been established by general industry practice and operating experience. This is particularly true since, in the event of seal failure, pressurized hydrogen inside the generator can escape through the frame/shaft interface possibly creating an explosive mixture outside the generator. Moreover, when a hydrogen leak occurs, the leaking seal does not reestablish itself until the generator is substantially degassed.
The present invention provides an accumulator design which is specifically tailored for inclusion in a generator seal oil system which includes a standby emergency seal oil pump. The accumulator is designed to maintain a minimum differential pressure across the generator seals at the required oil flow rate during a momentary reduction or interruption of supply oil flow.